Scoop on custom neck reamer...input wanted

konamtbiker

November 01, 2009 16:43

I would like to know the tolerance difference between a "match" fin reamer and plain Jane fin reamer. I'm guessing the big difference between the 2 would be that the match reamer would be closer to saami specs than the norm. If I am correct? How much closer to saami is it?

Another thing. I'm just doing to pull some numbers out of mid air.
Say i have reloaded for a 260 Remington with some nice new brass. lets assume that the bullet dia. is .264 and case-wall thickness is 15 thou. This would make the total diameter .294. Now lets say that I want to trim my neck and i take off a few thousands. Lets say to .290 If i want a custom neck on a reamer made. How much small would i request the neck of the reamer be made? I have heard .001-.003. what is best for most potential accuracy.

Here is another one!!

Now If i take that new reamer with a custom neck of .289, and by chance have it made into a 260 ackley. When i Fire form my nicely new trimmed neck, that have been trimmed to .290 Is case neck thickness going to grow or shrink due to fire forming?

Thanks in advance!

Kona.

All input is wanted. Ask questions back if im not making myself clear.

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  mrbruce

  November 02, 2009 05:22

  A match reamer is usually on the tight side of the saami scale....
  Tough to call the exact neck size to ask for, as sometimes between .001 and .003 below the loaded diameter will give up the best accuracy..
  Usually a bushing is called for to get the best possible fit for a particular rifle.
  A hunting rifle will usually have more clearance than a bench rest rifle will...
  
  Most all the Ackleys will shorten after they have been fired, and your neck thickness will increase to a point and then stop..

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  Tailgunner1954

  November 02, 2009 07:02

  quote:Originally posted by mrbruce
  as sometimes between .001 and .003 below the loaded diameter will give up the best accuracy..
  
  I believe that you mean you want the loaded diameter of the case NECK of the cartridge to be .001 to .003 BELOW (smaller) than diameter of the chamber neck. IOW if his turned necks, with a bullet seated, measure .290, than he want's his chamber to be in the .291-.294 range.
  
  If you pinch the case neck in the chamber, you will not like the experance.
  
  My only question for the OP is just how good are you, IE: are you good enough to notice/need the .1MOA reduction in group size.

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  WarGames

  November 02, 2009 07:13

  You generally want 0.003" to 0.004" total neck clearance.
  So your loaded cartridge at 0.290" would need a chamber neck at 0.293".
  No tighter.
  
  WG

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  mrbruce

  November 03, 2009 05:44

  Benchresters sure don't use that much clearance... in a hunting rifle yes.. But in a finely tuned custom rifle no way would I want that much slop...
  I don't go more than .002 clearance on my hunting rifles, and pistols..

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